46-516: A trans-Earth injection ( TEI ) is a propulsion maneuver used to set a spacecraft on a trajectory which will intersect the Earth 's sphere of influence , usually putting the spacecraft on a free return trajectory . The maneuver is performed by a rocket engine. The spacecraft is usually in a parking orbit around the Moon at the time of TEI, in which case the burn is timed so that its midpoint
92-608: A descent orbit , e.g. the Powered Descent Initiation maneuver used for Apollo lunar landings. In orbital mechanics , the Hohmann transfer orbit is an elliptical orbit used to transfer between two circular orbits of different altitudes, in the same plane . The orbital maneuver to perform the Hohmann transfer uses two engine impulses which move a spacecraft onto and off the transfer orbit. This maneuver
138-405: A spacecraft from one orbit to another and may, in certain situations, require less delta-v than a Hohmann transfer maneuver. The bi-elliptic transfer consists of two half elliptic orbits . From the initial orbit, a delta-v is applied boosting the spacecraft into the first transfer orbit with an apoapsis at some point r b {\displaystyle r_{b}} away from
184-690: A journey to Mars, an electrically powered ship might be able to carry 70% of its initial mass to the destination, while a chemical rocket could carry only a few percent. The idea of electric propulsion for spacecraft was introduced in 1911 by Konstantin Tsiolkovsky . Earlier, Robert Goddard had noted such a possibility in his personal notebook. On 15 May 1929, the Soviet research laboratory Gas Dynamics Laboratory (GDL) commenced development of electric rocket engines. Headed by Valentin Glushko , in
230-412: A lack of understanding of this effect led investigators to conclude that interplanetary travel would require completely impractical amounts of propellant, as without it, enormous amounts of energy are needed. In astrodynamics a gravity assist maneuver, gravitational slingshot or swing-by is the use of the relative movement and gravity of a planet or other celestial body to alter the trajectory of
276-491: A longer period. For a few space missions, such as those including a space rendezvous , high fidelity models of the trajectories are required to meet the mission goals. Calculating a "finite" burn requires a detailed model of the spacecraft and its thrusters. The most important of details include: mass , center of mass , moment of inertia , thruster positions, thrust vectors, thrust curves, specific impulse , thrust centroid offsets, and fuel consumption. In astronautics ,
322-450: A lower amount of total delta-v than a Hohmann transfer when the ratio of final to initial semi-major axis is 11.94 or greater, depending on the intermediate semi-major axis chosen. The idea of the bi-elliptical transfer trajectory was first published by Ary Sternfeld in 1934. A low energy transfer , or low energy trajectory , is a route in space which allows spacecraft to change orbits using very little fuel. These routes work in
368-536: A mathematical model it in most cases describes the effect of a maneuver on the orbit very well. The off-set of the velocity vector after the end of real burn from the velocity vector at the same time resulting from the theoretical impulsive maneuver is only caused by the difference in gravitational force along the two paths (red and black in figure 1) which in general is small. In the planning phase of space missions designers will first approximate their intended orbital changes using impulsive maneuvers that greatly reduces
414-507: A posigrade velocity increase of 1,000 m/s (3,300 ft/s). It was first performed by the Apollo 8 mission on December 25, 1968. It was last performed by the propulsion module of Chandrayaan-3 mission during 13 October 2023 Total 17 missions have performed such a maneuver. NASA has performed it the most (10 times), followed by Soviet Union (3 times), China (3 times), and India (once). These missions are in order, In 2004, from outside
460-482: A prescribed duration) or unsteady (pulsed firings accumulating to a desired impulse ). These classifications can be applied to all types of propulsion engines. Electrically powered rocket engines provide lower thrust compared to chemical rockets by several orders of magnitude because of the limited electrical power available in a spacecraft. A chemical rocket imparts energy to the combustion products directly, whereas an electrical system requires several steps. However,
506-615: A propellant. Electromagnetic thrusters accelerate ions either by the Lorentz force or by the effect of electromagnetic fields where the electric field is not in the direction of the acceleration. Types: A photonic drive interacts only with photons. Electrodynamic tethers are long conducting wires, such as one deployed from a tether satellite , which can operate on electromagnetic principles as generators , by converting their kinetic energy to electric energy , or as motors , converting electric energy to kinetic energy. Electric potential
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#1732779912103552-441: A spacecraft, typically in order to save propellant, time, and expense. Gravity assistance can be used to accelerate , decelerate and/or re-direct the path of a spacecraft. The "assist" is provided by the motion (orbital angular momentum ) of the gravitating body as it pulls on the spacecraft. The technique was first proposed as a mid-course maneuver in 1961, and used by interplanetary probes from Mariner 10 onwards, including
598-603: Is 500 to ~1000 seconds, but exceeds that of cold gas thrusters , monopropellant rockets , and even most bipropellant rockets . In the USSR , electrothermal engines entered use in 1971; the Soviet " Meteor-3 ", "Meteor-Priroda", "Resurs-O" satellite series and the Russian "Elektro" satellite are equipped with them. Electrothermal systems by Aerojet (MR-510) are currently used on Lockheed Martin A2100 satellites using hydrazine as
644-451: Is a sequence of orbital maneuvers during which two spacecraft , one of which is often a space station , arrive at the same orbit and approach to a very close distance (e.g. within visual contact). Rendezvous requires a precise match of the orbital velocities of the two spacecraft, allowing them to remain at a constant distance through orbital station-keeping . Rendezvous is commonly followed by docking or berthing , procedures which bring
690-420: Is controlled by power electronics . Electric thrusters typically use much less propellant than chemical rockets because they have a higher exhaust speed (operate at a higher specific impulse ) than chemical rockets. Due to limited electric power the thrust is much weaker compared to chemical rockets, but electric propulsion can provide thrust for a longer time. Electric propulsion was first demonstrated in
736-547: Is enough to take a spacecraft to the outer planets of the Solar System (with nuclear power ), but is insufficient for interstellar travel . An electric rocket with an external power source (transmissible through laser on the photovoltaic panels ) has a theoretical possibility for interstellar flight . However, electric propulsion is not suitable for launches from the Earth's surface, as it offers too little thrust. On
782-526: Is generated across a conductive tether by its motion through the Earth's magnetic field. The choice of the metal conductor to be used in an electrodynamic tether is determined by factors such as electrical conductivity , and density . Secondary factors, depending on the application, include cost, strength, and melting point. Some proposed propulsion methods apparently violate currently-understood laws of physics, including: Electric propulsion systems can be characterized as either steady (continuous firing for
828-563: Is opposite the Earth's location upon arrival. Uncrewed space probes have also performed this maneuver from the Moon starting with Luna 16 's direct ascent traverse from the lunar surface in 1970. On the Apollo missions, it was performed by the restartable Service Propulsion System (SPS) engine on the Service Module after the undocking of the (LM) Lunar Module if provided. An Apollo TEI burn lasted approximately 150 seconds, providing
874-427: Is required that the spacecraft rendezvous with the target, rather than performing a flyby, then the spacecraft must flip its orientation halfway through the journey, and decelerate the rest of the way. In the constant-thrust trajectory, the vehicle's acceleration increases during thrusting period, since the fuel use means the vehicle mass decreases. If, instead of constant thrust, the vehicle has constant acceleration,
920-430: Is the mathematical model of a maneuver as an instantaneous change in the spacecraft's velocity (magnitude and/or direction) as illustrated in figure 1. It is the limit case of a burn to generate a particular amount of delta-v, as the burn time tends to zero. In the physical world no truly instantaneous change in velocity is possible as this would require an "infinite force" applied during an "infinitely short time" but as
966-445: Is used in low thrust maneuvers, for example with ion engines , Hall-effect thrusters , and others. These types of engines have very high specific impulse (fuel efficiency) but currently are only available with fairly low absolute thrust. In astrodynamics orbit phasing is the adjustment of the time-position of spacecraft along its orbit , usually described as adjusting the orbiting spacecraft's true anomaly . A space rendezvous
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#17327799121031012-536: The Austro-Hungarian -born, German physicist and a founder of modern rocketry , who apparently first described the effect. The Oberth effect is used in a powered flyby or Oberth maneuver where the application of an impulse, typically from the use of a rocket engine, close to a gravitational body (where the gravity potential is low, and the speed is high) can give much more change in kinetic energy and final speed (i.e. higher specific energy ) than
1058-456: The Earth - Moon system and also in other systems, such as traveling between the satellites of Jupiter . The drawback of such trajectories is that they take much longer to complete than higher energy (more fuel) transfers such as Hohmann transfer orbits . Low energy transfer are also known as weak stability boundary trajectories, or ballistic capture trajectories. Low energy transfers follow special pathways in space, sometimes referred to as
1104-522: The Interplanetary Transport Network . Following these pathways allows for long distances to be traversed for little expenditure of delta-v . Orbital inclination change is an orbital maneuver aimed at changing the inclination of an orbiting body's orbit . This maneuver is also known as an orbital plane change as the plane of the orbit is tipped. This maneuver requires a change in the orbital velocity vector ( delta v ) at
1150-476: The Oberth effect is where the use of a rocket engine when travelling at high speed generates much more useful energy than one at low speed. Oberth effect occurs because the propellant has more usable energy (due to its kinetic energy on top of its chemical potential energy) and it turns out that the vehicle is able to employ this kinetic energy to generate more mechanical power. It is named after Hermann Oberth ,
1196-410: The central body . At this point, a second delta-v is applied sending the spacecraft into the second elliptical orbit with periapsis at the radius of the final desired orbit, where a third delta-v is performed, injecting the spacecraft into the desired orbit. While they require one more engine burn than a Hohmann transfer and generally requires a greater travel time, some bi-elliptic transfers require
1242-507: The orbital nodes (i.e. the point where the initial and desired orbits intersect, the line of orbital nodes is defined by the intersection of the two orbital planes). In general, inclination changes can require a great deal of delta-v to perform, and most mission planners try to avoid them whenever possible to conserve fuel. This is typically achieved by launching a spacecraft directly into the desired inclination, or as close to it as possible so as to minimize any inclination change required over
1288-496: The 1960s and is now a mature and widely used technology on spacecraft. American and Russian satellites have used electric propulsion for decades. As of 2019 , over 500 spacecraft operated throughout the Solar System use electric propulsion for station keeping , orbit raising, or primary propulsion. In the future, the most advanced electric thrusters may be able to impart a delta-v of 100 km/s (62 mi/s), which
1334-582: The Earth-Moon system, the Stardust probe comet dust return mission performed TEI after visiting Comet Wild 2 . This spacecraft or satellite related article is a stub . You can help Misplaced Pages by expanding it . Orbital maneuver In spaceflight , an orbital maneuver (otherwise known as a burn ) is the use of propulsion systems to change the orbit of a spacecraft . For spacecraft far from Earth (for example those in orbits around
1380-504: The Sun) an orbital maneuver is called a deep-space maneuver (DSM) . When a spacecraft is not conducting a maneuver, especially in a transfer orbit , it is said to be coasting . The Tsiolkovsky rocket equation, or ideal rocket equation, can be useful for analysis of maneuvers by vehicles using rocket propulsion. A rocket applies acceleration to itself (a thrust ) by expelling part of its mass at high speed. The rocket itself moves due to
1426-427: The complexity of finding the correct orbital transitions. Applying a low thrust over a longer period of time is referred to as a non-impulsive maneuver . 'Non-impulsive' refers to the momentum changing slowly over a long time, as in electrically powered spacecraft propulsion , rather than by a short impulse. Another term is finite burn , where the word "finite" is used to mean "non-zero", or practically, again: over
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1472-452: The conservation of momentum . The applied change in velocity of each maneuver is referred to as delta-v ( Δ v {\displaystyle \Delta \mathbf {v} \,} ). The delta-v for all the expected maneuvers are estimated for a mission are summarized in a delta-v budget . With a good approximation of the delta-v budget designers can estimate the propellant required for planned maneuvers. An impulsive maneuver
1518-472: The duration of the spacecraft life. Maximum efficiency of inclination change is achieved at apoapsis , (or apogee ), where orbital velocity v {\displaystyle v\,} is the lowest. In some cases, it may require less total delta v to raise the spacecraft into a higher orbit, change the orbit plane at the higher apogee, and then lower the spacecraft to its original altitude. Constant-thrust and constant-acceleration trajectories involve
1564-624: The early 1930s he created the world's first example of an electrothermal rocket engine. This early work by GDL has been steadily carried on and electric rocket engines were used in the 1960s on board the Voskhod 1 spacecraft and Zond-2 Mars probe. The first test of electric propulsion was an experimental ion engine carried on board the Soviet Zond 1 spacecraft in April 1964, however they operated erratically possibly due to problems with
1610-520: The early 2010s, many satellite manufacturers were offering electric propulsion options on their satellites—mostly for on-orbit attitude control —while some commercial communication satellite operators were beginning to use them for geosynchronous orbit insertion in place of traditional chemical rocket engines . These types of rocket-like reaction engines use electric energy to obtain thrust from propellant . Electric propulsion thrusters for spacecraft may be grouped into three families based on
1656-535: The engine thrust must decrease during the trajectory. This trajectory requires that the spacecraft maintain a high acceleration for long durations. For interplanetary transfers, days, weeks or months of constant thrusting may be required. As a result, there are no currently available spacecraft propulsion systems capable of using this trajectory. It has been suggested that some forms of nuclear (fission or fusion based) or antimatter powered rockets would be capable of this trajectory. More practically, this type of maneuver
1702-426: The high velocity and lower reaction mass expended for the same thrust allows electric rockets to run on less fuel. This differs from the typical chemical-powered spacecraft, where the engines require more fuel, requiring the spacecraft to mostly follow an inertial trajectory . When near a planet, low-thrust propulsion may not offset the gravitational force. An electric rocket engine cannot provide enough thrust to lift
1748-416: The other for almost three months. Electrically powered propulsion with a nuclear reactor was considered by Tony Martin for interstellar Project Daedalus in 1973, but the approach was rejected because of its thrust profile, the weight of equipment needed to convert nuclear energy into electricity, and as a result a small acceleration , which would take a century to achieve the desired speed. By
1794-582: The probe. The Zond 2 spacecraft also carried six Pulsed Plasma Thrusters (PPT) that served as actuators of the attitude control system. The PPT propulsion system was tested for 70 minutes on the 14 December 1964 when the spacecraft was 4.2 million kilometers from Earth. The first successful demonstration of an ion engine was NASA SERT-1 (Space Electric Rocket Test) spacecraft. It launched on 20 July 1964 and operated for 31 minutes. A follow-up mission launched on 3 February 1970, SERT-2. It carried two ion thrusters, one operated for more than five months and
1840-474: The propellant gas is then converted into kinetic energy by a nozzle of either solid material or magnetic fields. Low molecular weight gases (e.g. hydrogen, helium, ammonia) are preferred propellants for this kind of system. An electrothermal engine uses a nozzle to convert heat into linear motion, so it is a true rocket even though the energy producing the heat comes from an external source. Performance of electrothermal systems in terms of specific impulse (Isp)
1886-461: The same impulse applied further from the body for the same initial orbit. Since the Oberth maneuver happens in a very limited time (while still at low altitude), to generate a high impulse the engine necessarily needs to achieve high thrust (impulse is by definition the time multiplied by thrust). Thus the Oberth effect is far less useful for low-thrust engines, such as ion thrusters . Historically,
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1932-412: The spacecraft firing its engine in a prolonged constant burn. In the limiting case where the vehicle acceleration is high compared to the local gravitational acceleration, the spacecraft points straight toward the target (accounting for target motion), and remains accelerating constantly under high thrust until it reaches its target. In this high-thrust case, the trajectory approaches a straight line. If it
1978-420: The spacecraft into physical contact and create a link between them. Electrically powered spacecraft propulsion Spacecraft electric propulsion (or just electric propulsion ) is a type of spacecraft propulsion technique that uses electrostatic or electromagnetic fields to accelerate mass to high speed and thus generating thrust to modify the velocity of a spacecraft in orbit. The propulsion system
2024-476: The two Voyager probes' notable fly-bys of Jupiter and Saturn. Orbit insertion maneuvers leave a spacecraft in a destination orbit. In contrast, orbit injection maneuvers occur when a spacecraft enters a transfer orbit, e.g. trans-lunar injection (TLI), trans-Mars injection (TMI) and trans-Earth injection (TEI). These are generally larger than small trajectory correction maneuvers. Insertion, injection and sometimes initiation are used to describe entry into
2070-491: The type of force used to accelerate the ions of the plasma: If the acceleration is caused mainly by the Coulomb force (i.e. application of a static electric field in the direction of the acceleration) the device is considered electrostatic. Types: The electrothermal category groups devices that use electromagnetic fields to generate a plasma to increase the temperature of the bulk propellant. The thermal energy imparted to
2116-525: Was named after Walter Hohmann , the German scientist who published a description of it in his 1925 book Die Erreichbarkeit der Himmelskörper ( The Accessibility of Celestial Bodies ). Hohmann was influenced in part by the German science fiction author Kurd Laßwitz and his 1897 book Two Planets . In astronautics and aerospace engineering , the bi-elliptic transfer is an orbital maneuver that moves
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